1. Field of the Invention
The present invention relates to a semiconductor device and a trimming method of the same, and more particularly, to a semiconductor device having a trimming circuit capable of reducing the number of external terminals required for trimming some parts of the semiconductor device and a trimming method of the same.
2. Description of the Related Art
Generally, in the manufacturing process of semiconductor devices, characteristics of the semiconductor devices may vary due to the variations of parts in the circuits caused by the variation of the manufacturing process. Because of this feature of a semiconductor device, a trimming method is conventionally used to maintain the characteristics especially when the characteristics are required to be highly accurate.
As an example of a conventional semiconductor device, FIG. 3 shows a schematic circuit diagram of a conventional semiconductor device 1 that includes an auxiliary voltage regulator circuit 10 and a voltage regulator circuit 20.
The auxiliary voltage regulator circuit 10 includes a comparator 11 and outputs an output voltage Vs to supply power to an internal circuit (not shown) and a reference voltage circuit 22 of the voltage regulator circuit 20. The auxiliary voltage regulator circuit 10 further includes a resistor R1 as a first trimming unit so as to adjust the output voltage Vs. The comparator 11 operates such that a divided voltage divided from the output voltage Vs by the resistor R1 and a resistor R2 is equal to a reference voltage Vr1 applied to the comparator 11. Further, a test terminal T1 is provided as an external terminal of the semiconductor device 1 for performing a first trimming adjustment. The voltage regulator circuit 20 includes a comparator 21, the reference voltage circuit 22, and an overheat protection circuit 23 and outputs an output voltage Vo. The comparator 21 operates such that a divided voltage divided from the output voltage Vo by resistors R3 and R4 is equal to a prescribed reference voltage Vr2 output from the reference voltage circuit 22. Further, a test terminal T2 extending from the overheat protection circuit 23 is provided as another external terminal. A detailed description of the overheat protection circuit as well as the connection with the test terminal T2 is provided below with reference to FIG. 4.
FIG. 4 is a schematic circuit diagram of the overheat protection circuit 23 in FIG. 3. As shown in FIG. 4, the overheat protection circuit 23 includes a reference voltage source 25 generating a reference voltage Vr3, a temperature detection diode D1, a constant current source I1, and a comparator 24. The reference voltage source 25 outputting an adjustable reference voltage Vr3 is provided as a second trimming unit so as to set a temperature at which the overheat protection circuit 23 is activated. The test terminal T2 for performing a second trimming adjustment is provided as an external terminal of the semiconductor device 1.
To perform the first trimming adjustment to adjust the output voltage Vs output from the auxiliary voltage regulator 10, the voltage at the test terminal T1 is measured. Then, a trimming is performed with respect to the resistor R1 of the first trimming unit based on the measured voltage.
To perform the second trimming adjustment to adjust the temperature at which the overheat protection circuit 23 is activated, a voltage applied to the test terminal T2 is gradually changed to detect a voltage at which the overheat protection circuit 23 is activated. The detected voltage is adjusted by a trimming voltage determined based on the difference between the chip temperature of the semiconductor device when this test is performed and the chip temperature at which the overheat protection circuit is to be activated. Then the reference voltage Vr3 of the second trimming unit is adjusted so as to be equal to the adjusted voltage.
Unfortunately, as described above, in a conventional trimming method, each test terminal constituting an external terminal is always necessary for the corresponding trimming portion of the semiconductor device.
To solve the problem, a method reducing the number of terminals used for trimming is disclosed in, for example, Japanese Patent Application Publication No. H08-204582. According to the Patent Document, the number of terminal is reduced by providing a decoder and data from a trimming circuit is decoded by the decoder and then output from an external terminal. This method may be advantageously employed when there are many trimming portions in the semiconductor device, but may be disadvantageous particularly when there are only a few trimming portions in the semiconductor device. Namely, when this method is employed in small-scale semiconductor devices, the circuit scales may be rather increased due to the additional control circuit including the decoder and control terminals connected from the control circuit. Therefore, this trimming method may not fit a small-scale semiconductor device.
Generally and unfortunately, in a semiconductor device, when the number of external terminals increases, the area of the semiconductor chip accordingly increases and the cost is also increased. Especially, the smaller the area of the semiconductor chip is, the more strongly is the semiconductor chip affected by the increase of the external terminals. In addition, the number of the external terminals is a major factor in determining the package size of the semiconductor device. Namely, when the number of the external terminals increases, the package size becomes larger accordingly and the cost is also increased. Further disadvantageously, a larger area for mounting parts becomes necessary and as a result, the size of a system using the semiconductor device may be increased.